The invention relates to a device for mounting and removing a cutter at the end of the cutter shaft of a cutter dredge, the cutter boss being provided with an inner screw-thread and the cutter shaft being provided with an outer screw-thread.
When dredgers are fitted with a cutter head, better known as a cutter, said cutter head is usually replaceable by a new one. It is for this purpose that the cutter is provided with an inner screw-thread and the cutter shaft is provided at the end thereof with an outer screw-thread.
The cutter may thus be screwed on said shaft till the cutter boss edge meets a collar on the shaft. The boss bottom can also meet the shaft end.
It is clear that under the action of the butting load on the cutter knives or teeth, said cutter is generally clamped very tightly on the shaft, and cannot generally be screwed off with the available torque from the motor driving the cutter shaft.
To obviate the above-defined drawback, there is generally mounted between the boss and a stop on the cutter shaft, a number of small blocks or a flanged plug. When replacing the cutter, the blocks or the flange are cut-through in such a way that the screw-thread load is removed and the cutter can easily be screwed off. Present-day suction dredges with large dredging capacity use in general blocks made of steel, also called cutting blocks. Cutting plugs between the cutter shaft end and boss bottom are less frequently used.
The disadvantages of the above-mentioned operating method are as follows:
(a) the cutting-through of said cutting blocks or cutting plug is a time-consuming operation which results in a long idle time of the dredge;
(b) when cutting through the cutting blocks or the cutting plug, there is a severe danger of damaging the cutter shaft;
(c) through the space present between the cutting blocks, sand and water may enter the screw-thread from the cutter and cutter shaft. Such entry of water and sand is the cause of corrosion and notch effect which may result in premature shaft breakage;
(d) after every removal of the cutter, the screw-thread must to be cleaned and protected;
(e) when removing the cutter, new blocks or a new cutting plug must to be arranged each time. Even if the protecting plug can be made more water-tight, it is also more expensive.